Joined Jun 2012
RCTigerMotor MT3506 erroneous advertised data
I'm writing this to warn others, express my dissatisfaction, and publicize the poor laboratory practices of Rc Tiger Motor.
I had my eye on their MT3506 for a while because they published crazy awesome static lift efficiency. Here's the data they publish:
Look at the 13x4.5 prop section. For 730 g of thrust, they're saying it's getting 15.66 g/W! This is unbelievable! Well it's too good to be true as the old addage suggests.
I acquired a few of these for my own purposes. I put them on a thurst stand to see if I could duplicate these readings. The best I achieve was about 10-11 g/W at 500 g of thrust. This is quite a bit different, and actually sub par. I was disappointed. Curiously, they put another plot on their website from some other user on rcgroups. This plot itself disagrees with their tabular data, and agrees with my data! Either they're publishing false data in the table, or their measurements are wrong. After working in an engineering laboratory environment for about 12 years, the biggest lesson I've learned is, "always question the instrumentation." A colleague of mine has his own mantra, "all sensors suck." It turns out this is true in this case.
I corresponded with RC Tiger Motor to acquire the precise details of how they made their measurements. I found that it was identical to my thrust stand except they were using a DC power supply instead of a battery.
This is where the fault lies. My suspicion is they're using the voltage and current readout of the DC power supply to calculate power. This is poor laboratory practice. Doing so is not in any way an accurate measurement of power, which is required to calculate static thrust efficiency, g/W. I found that they are using a Mastech power supply. I have one of these myself, b/c the price is so low. On my unit, I've noticed first hand the garbage reported by the current readout. In one case I was actually pulling 6 amps and it read 0.3! If I were to use this readout to calculate power, I'd be completely wrong.
Lesson learned I suppose.
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